Discuss different levels of data abstraction

Several levels of data abstraction are maintained to simplify users interaction with the system:

(i) Physical level: The lowest level of abstraction describes how data are actually stored. It describes complex low-level data structures in detail.

(ii) Logical level: The next higher level of abstraction describes what data stored in database, and what relationships exist among those data. The logical level thus describes the entire database in terms of a number of relatively simple structures.

For Example:

create table customer (

customer_id varchar (10),

customer_name varchar (35),

customer_street varchar (20);

salary number (10, 2));

(iii) View level: The highest level of abstraction describe only part of the entire database. Although the logical level uses simpler structures, complexity remains because of the variety of the information stored in a large database. Many users of the database system do not need all this information; instead they need to access only a part of the database. The view level of abstraction exists to simplify their interaction with the system. The system may provide many views for the same database. In addition to hiding details, the views also provide a security mechanism to prevent users from accessing certain part of the database.